#!/usr/bin/env python        range_ahead.py
# BEGIN ALL
import rospy
from sensor_msgs.msg import LaserScan

# BEGIN MEASUREMENT
def scan_callback(msg):
  range_ahead = msg.ranges[len(msg.ranges)/2]
  print len(msg.ranges)
  print "range ahead: %0.6f" % range_ahead

  # END MEASUREMENT

rospy.init_node('range_ahead')
scan_sub = rospy.Subscriber('scan', LaserScan, scan_callback)
rospy.spin()
# END ALL